Instructions To Mark Beginning and End Of Non Transactional Code Region Requiring Write Back To Persistent Storage

ABSTRACT

A processor in described having an interface to non volatile random access memory and logic circuitry. The logic circuitry is to identify cache lines modified by a transaction which views the volatile random access memory as the transaction&#39;s persistence storage. The logic circuitry is also to identify cache lines modified by a software process other than a transaction that also views said non volatile random access memory as persistence storage.

FIELD OF THE INVENTION

This invention relates generally to the field of computer systems. More particularly, the invention relates to an apparatus and method for implementing a multi-level memory hierarchy including a non-volatile memory tier.

DESCRIPTION OF THE RELATED ART

A. Current Memory and Storage Configurations

One of the limiting factors for computer innovation today is memory and storage technology. In conventional computer systems, system memory (also known as main memory, primary memory, executable memory) is typically implemented by dynamic random access memory (DRAM). DRAM-based memory consumes power even when no memory reads or writes occur because it must constantly recharge internal capacitors. DRAM-based memory is volatile, which means data stored in DRAM memory is lost once the power is removed. Conventional computer systems also rely on multiple levels of caching to improve performance. A cache is a high speed memory positioned between the processor and system memory to service memory access requests faster than they could be serviced from system memory. Such caches are typically implemented with static random access memory (SRAM). Cache management protocols may be used to ensure that the most frequently accessed data and instructions are stored within one of the levels of cache, thereby reducing the number of memory access operations and improving performance.

With respect to mass storage (also known as secondary storage or disk storage), conventional mass storage devices typically include magnetic media (e.g., hard disk drives), optical media (e.g., compact disc (CD) drive, digital versatile disc (DVD), etc.), holographic media, and/or mass-storage flash memory (e.g., solid state drives (SSDs), removable flash drives, etc.). Generally, these storage devices are considered Input/Output (I/O) devices because they are accessed by the processor through various I/O adapters that implement various I/O protocols. These I/O adapters and I/O protocols consume a significant amount of power and can have a significant impact on the die area and the form factor of the platform. Portable or mobile devices (e.g., laptops, netbooks, tablet computers, personal digital assistant (PDAs), portable media players, portable gaming devices, digital cameras, mobile phones, smartphones, feature phones, etc.) that have limited battery life when not connected to a permanent power supply may include removable mass storage devices (e.g., Embedded Multimedia Card (eMMC), Secure Digital (SD) card) that are typically coupled to the processor via low-power interconnects and I/O controllers in order to meet active and idle power budgets.

With respect to firmware memory (such as boot memory (also known as BIOS flash)), a conventional computer system typically uses flash memory devices to store persistent system information that is read often but seldom (or never) written to. For example, the initial instructions executed by a processor to initialize key system components during a boot process (Basic Input and Output System (BIOS) images) are typically stored in a flash memory device. Flash memory devices that are currently available in the market generally have limited speed (e.g., 50 MHz). This speed is further reduced by the overhead for read protocols (e.g., 2.5 MHz). In order to speed up the BIOS execution speed, conventional processors generally cache a portion of BIOS code during the Pre-Extensible Firmware Interface (PEI) phase of the boot process. The size of the processor cache places a restriction on the size of the BIOS code used in the PEI phase (also known as the “PEI BIOS code”).

B. Phase-Change Memory (PCM) and Related Technologies

Phase-change memory (PCM), also sometimes referred to as phase change random access memory (PRAM or PCRAM), PCME, Ovonic Unified Memory, or Chalcogenide RAM (C-RAM), is a type of non-volatile computer memory which exploits the unique behavior of chalcogenide glass. As a result of heat produced by the passage of an electric current, chalcogenide glass can be switched between two states: crystalline and amorphous. Recent versions of PCM can achieve two additional distinct states.

PCM provides higher performance than flash because the memory element of PCM can be switched more quickly, writing (changing individual bits to either 1 or 0) can be done without the need to first erase an entire block of cells, and degradation from writes is slower (a PCM device may survive approximately 100 million write cycles; PCM degradation is due to thermal expansion during programming, metal (and other material) migration, and other mechanisms).

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and accompanying drawings are used to illustrate embodiments of the invention. In the drawings:

FIG. 1 illustrates a cache and system memory arrangement according to one embodiment of the invention;

FIG. 2 illustrates a memory and storage hierarchy employed in one embodiment of the invention;

FIG. 3 illustrates a computer system on which embodiments of the invention may be implemented;

FIG. 4 illustrates a transaction process;

FIG. 5 illustrates a processor having special hardware to track changes made to cache;

FIG. 6 shows a process that uses the special hardware of FIG. 5 to write non transactional data changes to persistence storage;

FIG. 7 shows an integrated process that illustrates that the special hardware of FIG. 5 can be used to support by transactional roll backs and non transactional writes to persistence;

FIG. 8 shows a compilation process.

DETAILED DESCRIPTION

In the following description, numerous specific details such as logic implementations, opcodes, means to specify operands, resource partitioning/sharing/duplication implementations, types and interrelationships of system components, and logic partitioning/integration choices are set forth in order to provide a more thorough understanding of the present invention. It will be appreciated, however, by one skilled in the art that the invention may be practiced without such specific details. In other instances, control structures, gate level circuits and full software instruction sequences have not been shown in detail in order not to obscure the invention. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation.

References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

In the following description and claims, the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. “Coupled” is used to indicate that two or more elements, which may or may not be in direct physical or electrical contact with each other, co-operate or interact with each other. “Connected” is used to indicate the establishment of communication between two or more elements that are coupled with each other.

Bracketed text and blocks with dashed borders (e.g., large dashes, small dashes, dot-dash, dots) are sometimes used herein to illustrate optional operations/components that add additional features to embodiments of the invention. However, such notation should not be taken to mean that these are the only options or optional operations/components, and/or that blocks with solid borders are not optional in certain embodiments.

INTRODUCTION

Memory capacity and performance requirements continue to increase with an increasing number of processor cores and new usage models such as virtualization. In addition, memory power and cost have become a significant component of the overall power and cost, respectively, of electronic systems.

Some embodiments solve the above challenges by intelligently subdividing the performance requirement and the capacity requirement between memory technologies. The focus of this approach is on providing performance with a relatively small amount of relatively higher-speed memory such as DRAM while implementing the bulk of the system memory using significantly denser non volatile random access memory (NVRAM). Embodiments of the invention described below define platform configurations that enable hierarchical memory subsystem organizations for the use of NVRAM. The use of NVRAM in the memory hierarchy also enables new usages such as expanded boot space and mass storage implementations.

FIG. 1 illustrates a cache and system memory arrangement according to embodiments of the invention. Specifically, FIG. 1 shows a memory hierarchy including a set of internal processor caches 120, “near memory” acting as a far memory cache 121, which may include both internal cache(s) 106 and external caches 107-109, and “far memory” 122. One particular type of memory which may be used for “far memory” in some embodiments of the invention is non-volatile random access memory (“NVRAM”). As such, an overview of NVRAM is provided below, followed by an overview of far memory and near memory.

A. Non-Volatile Random Access Memory (“NVRAM”)

There are many possible technology choices for NVRAM, including PCM, Phase Change Memory and Switch (PCMS) (the latter being a more specific implementation of the former), byte-addressable persistent memory (BPRAM), storage class memory (SCM), universal memory, Ge2Sb2Te5, programmable metallization cell (PMC), resistive memory (RRAM), RESET (amorphous) cell, SET (crystalline) cell, PCME, Ovshinsky memory, ferroelectric memory (also known as polymer memory and poly(N-vinylcarbazole)), ferromagnetic memory (also known as Spintronics, SPRAM (spin-transfer torque RAM), STRAM (spin tunneling RAM), magnetoresistive memory, magnetic memory, magnetic random access memory (MRAM)), and Semiconductor-oxide-nitride-oxide-semiconductor (SONOS, also known as dielectric memory).

NVRAM has the following characteristics:

(1) It maintains its content even if power is removed, similar to FLASH memory used in solid state disks (SSD), and different from SRAM and DRAM which are volatile;

(2) lower power consumption than volatile memories such as SRAM and DRAM;

(3) random access similar to SRAM and DRAM (also known as randomly addressable);

(4) rewritable and erasable at a lower level of granularity (e.g., byte level) than FLASH found in SSDs (which can only be rewritten and erased a “block” at a time—minimally 64 Kbyte in size for NOR FLASH and 16 Kbyte for NAND FLASH);

(5) used as a system memory and allocated all or a portion of the system memory address space;

(6) capable of being coupled to the processor over a bus using a protocol that supports identifiers (IDs) to support out-of-order operation) and allowing access at a level of granularity small enough to support operation of the NVRAM as system memory (e.g., cache line size such as 64 or 128 byte). For example, the bus may be a non out-of-order memory bus (e.g., a DDR bus such as DDR3, DDR4, etc.). As another example, the bus may be PCI express (PCIE) bus, desktop management interface (DMI) bus, or any other type of bus utilizing an out-of-order protocol and a small enough payload size (e.g., cache line size such as 64 or 128 byte); and

(7) one or more of the following:

-   -   a) faster write speed than non-volatile memory/storage         technologies such as FLASH;     -   b) very high read speed (faster than FLASH and near or         equivalent to DRAM read speeds);     -   c) directly writable (rather than requiring erasing (overwriting         with 1s) before writing data like FLASH memory used in SSDs);     -   d) a greater number of writes before failure (more than boot ROM         and FLASH used in SSDs); and/or

As mentioned above, in contrast to FLASH memory, which must be rewritten and erased a complete “block” at a time, the level of granularity at which NVRAM is accessed in any given implementation may depend on the particular memory controller and the particular memory bus or other type of bus to which the NVRAM is coupled. For example, in some implementations where NVRAM is used as system memory, the NVRAM may be accessed at the granularity of a cache line (e.g., a 64-byte or 128-Byte cache line), notwithstanding an inherent ability to be accessed at the granularity of a byte, because cache line is the level at which the memory subsystem accesses memory. Thus, when NVRAM is deployed within a memory subsystem, it may be accessed at the same level of granularity as the DRAM (e.g., the “near memory”) used in the same memory subsystem. Even so, the level of granularity of access to the NVRAM by the memory controller and memory bus or other type of bus is smaller than that of the block size used by Flash and the access size of the I/O subsystem's controller and bus.

NVRAM may also incorporate wear leveling algorithms to account for the fact that the storage cells at the far memory level begin to wear out after a number of write accesses, especially where a significant number of writes may occur such as in a system memory implementation. Since high cycle count blocks are most likely to wear out in this manner, wear leveling spreads writes across the far memory cells by swapping addresses of high cycle count blocks with low cycle count blocks. Note that most address swapping is typically transparent to application programs_because it is handled by hardware, lower-level software (e.g., a low level driver or operating system), or a combination of the two.

B. Far Memory

The far memory 122 of some embodiments of the invention is implemented with NVRAM, but is not necessarily limited to any particular memory technology. Far memory 122 is distinguishable from other instruction and data memory/storage technologies in terms of its characteristics and/or its application in the memory/storage hierarchy. For example, far memory 122 is different from:

-   -   1) static random access memory (SRAM) which may be used for         level 0 and level 1 internal processor caches 101 a-b, 102 a-b,         103 a-b, 103 a-b, and 104 a-b dedicated to each of the processor         cores 101-104, respectively, and lower level cache (LLC) 105         shared by the processor cores;     -   2) dynamic random access memory (DRAM) configured as a cache 106         internal to the processor 100 (e.g., on the same die as the         processor 100) and/or configured as one or more caches 107-109         external to the processor (e.g., in the same or a different         package from the processor 100); and     -   3) FLASH memory/magnetic disk/optical disc applied as mass         storage (not shown); and     -   4) memory such as FLASH memory or other read only memory (ROM)         applied as firmware memory (which can refer to boot ROM, BIOS         Flash, and/or TPM Flash). (not shown).

Far memory 122 may be used as instruction and data storage that is directly addressable by a processor 100 and is able to sufficiently keep pace with the processor 100 in contrast to FLASH/magnetic disk/optical disc applied as mass storage. Moreover, as discussed above and described in detail below, far memory 122 may be placed on a memory bus and may communicate directly with a memory controller that, in turn, communicates directly with the processor 100.

Far memory 122 may be combined with other instruction and data storage technologies (e.g., DRAM) to form hybrid memories (also known as Co-locating PCM and DRAM; first level memory and second level memory; FLAM (FLASH and DRAM)). Note that at least some of the above technologies, including PCM/PCMS may be used for mass storage instead of, or in addition to, system memory, and need not be random accessible, byte addressable or directly addressable by the processor when applied in this manner.

For convenience of explanation, most of the remainder of the application will refer to “NVRAM” or, more specifically, “PCM,” or “PCMS” as the technology selection for the far memory 122. As such, the terms NVRAM, PCM, PCMS, and far memory may be used interchangeably in the following discussion. However it should be realized, as discussed above, that different technologies may also be utilized for far memory. Also, that NVRAM is not limited for use as far memory.

C. Near Memory

“Near memory” 121 is an intermediate level of memory configured in front of a far memory 122 that has lower read/write access latency relative to far memory and/or more symmetric read/write access latency (i.e., having read times which are roughly equivalent to write times). In some embodiments, the near memory 121 has significantly lower write latency than the far memory 122 but similar (e.g., slightly lower or equal) read latency; for instance the near memory 121 may be a volatile memory such as volatile random access memory (VRAM) and may comprise a DRAM or other high speed capacitor-based memory. Note, however, that the underlying principles of the invention are not limited to these specific memory types. Additionally, the near memory 121 may have a relatively lower density and/or may be more expensive to manufacture than the far memory 122.

In one embodiment, near memory 121 is configured between the far memory 122 and the internal processor caches 120. In some of the embodiments described below, near memory 121 is configured as one or more memory-side caches (MSCs) 107-109 to mask the performance and/or usage limitations of the far memory including, for example, read/write latency limitations and memory degradation limitations. In these implementations, the combination of the MSC 107-109 and far memory 122 operates at a performance level which approximates, is equivalent or exceeds a system which uses only DRAM as system memory. As discussed in detail below, although shown as a “cache” in FIG. 1, the near memory 121 may include modes in which it performs other roles, either in addition to, or in lieu of, performing the role of a cache.

Near memory 121 can be located on the processor die (as cache(s) 106) and/or located external to the processor die (as caches 107-109) (e.g., on a separate die located on the CPU package, located outside the CPU package with a high bandwidth link to the CPU package, for example, on a memory dual in-line memory module (DIMM), a riser/mezzanine, or a computer motherboard). The near memory 121 may be coupled in communicate with the processor 100 using a single or multiple high bandwidth links, such as DDR or other high bandwidth links (as described in detail below).

An Exemplary System Memory Allocation Scheme

FIG. 1 illustrates how various levels of caches 101-109 are configured with respect to a system physical address (SPA) space 116-119 in embodiments of the invention. As mentioned, this embodiment comprises a processor 100 having one or more cores 101-104, with each core having its own dedicated upper level cache (L0) 101 a-104 a and mid-level cache (MLC) (L1) cache 101 b-104 b. The processor 100 also includes a shared LLC 105. The operation of these various cache levels are well understood and will not be described in detail here.

The caches 107-109 illustrated in FIG. 1 may be dedicated to a particular system memory address range or a set of non-contiguous address ranges. For example, cache 107 is dedicated to acting as an MSC for system memory address range #1 116 and caches 108 and 109 are dedicated to acting as MSCs for non-overlapping portions of system memory address ranges #2 117 and #3 118. The latter implementation may be used for systems in which the SPA space used by the processor 100 is interleaved into an address space used by the caches 107-109 (e.g., when configured as MSCs). In some embodiments, this latter address space is referred to as a memory channel address (MCA) space. In one embodiment, the internal caches 101 a-106 perform caching operations for the entire SPA space.

System memory as used herein is memory which is visible to and/or directly addressable by software executed on the processor 100; while the cache memories 101 a-109 may operate transparently to the software in the sense that they do not form a directly-addressable portion of the system address space, but the cores may also support execution of instructions to allow software to provide some control (configuration, policies, hints, etc.) to some or all of the cache(s). The subdivision of system memory into regions 116-119 may be performed manually as part of a system configuration process (e.g., by a system designer) and/or may be performed automatically by software.

In one embodiment, the system memory regions 116-119 are implemented using far memory (e.g., PCM) and, in some embodiments, near memory configured as system memory. System memory address range #4 represents an address range which is implemented using a higher speed memory such as DRAM which may be a near memory configured in a system memory mode (as opposed to a caching mode).

FIG. 2 illustrates a memory/storage hierarchy 140 and different configurable modes of operation for near memory 144 and NVRAM according to embodiments of the invention. The memory/storage hierarchy 140 has multiple levels including (1) a cache level 150 which may include processor caches 150A (e.g., caches 101A-105 in FIG. 1) and optionally near memory as cache for far memory 150B (in certain modes of operation as described herein), (2) a system memory level 151 which may include far memory 151B (e.g., NVRAM such as PCM) when near memory is present (or just NVRAM as system memory 174 when near memory is not present), and optionally near memory operating as system memory 151A (in certain modes of operation as described herein), (3) a mass storage level 152 which may include a flash/magnetic/optical mass storage 152B and/or NVRAM mass storage 152A (e.g., a portion of the NVRAM 142); and (4) a firmware memory level 153 that may include BIOS flash 170 and/or BIOS NVRAM 172 and optionally trusted platform module (TPM) NVRAM 173.

As indicated, near memory 144 may be implemented to operate in a variety of different modes including: a first mode in which it operates as a cache for far memory (near memory as cache for FM 150B); a second mode in which it operates as system memory 151A and occupies a portion of the SPA space (sometimes referred to as near memory “direct access” mode); and one or more additional modes of operation such as a scratchpad memory 192 or as a write buffer 193. In some embodiments of the invention, the near memory is partitionable, where each partition may concurrently operate in a different one of the supported modes; and different embodiments may support configuration of the partitions (e.g., sizes, modes) by hardware (e.g., fuses, pins), firmware, and/or software (e.g., through a set of programmable range registers within the MSC controller 124 within which, for example, may be stored different binary codes to identify each mode and partition).

System address space A 190 in FIG. 2 is used to illustrate operation when near memory is configured as a MSC for far memory 150B. In this configuration, system address space A 190 represents the entire system address space (and system address space B 191 does not exist). Alternatively, system address space B 191 is used to show an implementation when all or a portion of near memory is assigned a portion of the system address space. In this embodiment, system address space B 191 represents the range of the system address space assigned to the near memory 151A and system address space A 190 represents the range of the system address space assigned to NVRAM 174.

In addition, when acting as a cache for far memory 150B, the near memory 144 may operate in various sub-modes under the control of the MSC controller 124. In each of these modes, the near memory address space (NMA) is transparent to software in the sense that the near memory does not form a directly-addressable portion of the system address space. These modes include but are not limited to the following:

(1) Write-Back Caching Mode: In this mode, all or portions of the near memory acting as a FM cache 150B is used as a cache for the NVRAM far memory (FM) 151B. While in write-back mode, every write operation is directed initially to the near memory as cache for FM 150B (assuming that the cache line to which the write is directed is present in the cache). A corresponding write operation is performed to update the NVRAM FM 151B only when the cache line within the near memory as cache for FM 150B is to be replaced by another cache line (in contrast to write-through mode described below in which each write operation is immediately propagated to the NVRAM FM 151B).

(2) Near Memory Bypass Mode: In this mode all reads and writes bypass the NM acting as a FM cache 150B and go directly to the NVRAM FM 151B. Such a mode may be used, for example, when an application is not cache friendly or requires data to be committed to persistence at the granularity of a cache line. In one embodiment, the caching performed by the processor caches 150A and the NM acting as a FM cache 150B operate independently of one another. Consequently, data may be cached in the NM acting as a FM cache 150B which is not cached in the processor caches 150A (and which, in some cases, may not be permitted to be cached in the processor caches 150A) and vice versa. Thus, certain data which may be designated as “uncacheable” in the processor caches may be cached within the NM acting as a FM cache 150B.

(3) Near Memory Read-Cache Write Bypass Mode: This is a variation of the above mode where read caching of the persistent data from NVRAM FM 151B is allowed (i.e., the persistent data is cached in the near memory as cache for far memory 150B for read-only operations). This is useful when most of the persistent data is “Read-Only” and the application usage is cache-friendly.

(4) Near Memory Read-Cache Write-Through Mode: This is a variation of the near memory read-cache write bypass mode, where in addition to read caching, write-hits are also cached. Every write to the near memory as cache for FM 150B causes a write to the FM 151B. Thus, due to the write-through nature of the cache, cache-line persistence is still guaranteed.

When acting in near memory direct access mode, all or portions of the near memory as system memory 151A are directly visible to software and form part of the SPA space. Such memory may be completely under software control. Such a scheme may create a non-uniform memory address (NUMA) memory domain for software where it gets higher performance from near memory 144 relative to NVRAM system memory 174. By way of example, and not limitation, such a usage may be employed for certain high performance computing (HPC) and graphics applications which require very fast access to certain data structures.

In an alternate embodiment, the near memory direct access mode is implemented by “pinning” certain cache lines in near memory (i.e., cache lines which have data that is also concurrently stored in NVRAM 142). Such pinning may be done effectively in larger, multi-way, set-associative caches.

FIG. 2 also illustrates that a portion of the NVRAM 142 may be used as firmware memory. For example, the BIOS NVRAM 172 portion may be used to store BIOS images (instead of or in addition to storing the BIOS information in BIOS flash 170). The BIOS NVRAM portion 172 may be a portion of the SPA space and is directly addressable by software executed on the processor cores 101-104, whereas the BIOS flash 170 is addressable through the I/O subsystem 115. As another example, a trusted platform module (TPM) NVRAM 173 portion may be used to protect sensitive system information (e.g., encryption keys).

Thus, as indicated, the NVRAM 142 may be implemented to operate in a variety of different modes, including as far memory 151B (e.g., when near memory 144 is present/operating, whether the near memory is acting as a cache for the FM via a MSC control 124 or not (accessed directly after cache(s) 101A-105 and without MSC control 124)); just NVRAM system memory 174 (not as far memory because there is no near memory present/operating; and accessed without MSC control 124); NVRAM mass storage 152A; BIOS NVRAM 172; and TPM NVRAM 173. While different embodiments may specify the NVRAM modes in different ways, FIG. 3 describes the use of a decode table 333.

FIG. 3 illustrates an exemplary computer system 300 on which embodiments of the invention may be implemented. The computer system 300 includes a processor 310 and memory/storage subsystem 380 with a NVRAM 142 used for both system memory, mass storage, and optionally firmware memory. In one embodiment, the NVRAM 142 comprises the entire system memory and storage hierarchy used by computer system 300 for storing data, instructions, states, and other persistent and non-persistent information. As previously discussed, NVRAM 142 can be configured to implement the roles in a typical memory and storage hierarchy of system memory, mass storage, and firmware memory, TPM memory, and the like. In the embodiment of FIG. 3, NVRAM 142 is partitioned into FM 151B, NVRAM mass storage 152A, BIOS NVRAM 173, and TMP NVRAM 173. Storage hierarchies with different roles are also contemplated and the application of NVRAM 142 is not limited to the roles described above.

By way of example, operation while the near memory as cache for FM 150B is in the write-back caching is described. In one embodiment, while the near memory as cache for FM 150B is in the write-back caching mode mentioned above, a read operation will first arrive at the MSC controller 124 which will perform a look-up to determine if the requested data is present in the near memory acting as a cache for FM 150B (e.g., utilizing a tag cache 342). If present, it will return the data to the requesting CPU, core 101-104 or I/O device through I/O subsystem 115. If the data is not present, the MSC controller 124 will send the request along with the system memory address to an NVRAM controller 332. The NVRAM controller 332 will use the decode table 333 to translate the system memory address to an NVRAM physical device address (PDA) and direct the read operation to this region of the far memory 151B. In one embodiment, the decode table 333 includes an address indirection table (AIT) component which the NVRAM controller 332 uses to translate between system memory addresses and NVRAM PDAs. In one embodiment, the AIT is updated as part of the wear leveling algorithm implemented to distribute memory access operations and thereby reduce wear on the NVRAM FM 151B. Alternatively, the AIT may be a separate table stored within the NVRAM controller 332.

Upon receiving the requested data from the NVRAM FM 151B, the NVRAM controller 332 will return the requested data to the MSC controller 124 which will store the data in the MSC near memory acting as an FM cache 150B and also send the data to the requesting processor core 101-104, or I/O Device through I/O subsystem 115. Subsequent requests for this data may be serviced directly from the near memory acting as a FM cache 150B until it is replaced by some other NVRAM FM data.

As mentioned, in one embodiment, a memory write operation also first goes to the MSC controller 124 which writes it into the MSC near memory acting as a FM cache 150B. In write-back caching mode, the data may not be sent directly to the NVRAM FM 151B when a write operation is received. For example, the data may be sent to the NVRAM FM 151B only when the location in the MSC near memory acting as a FM cache 150B in which the data is stored must be re-used for storing data for a different system memory address. When this happens, the MSC controller 124 notices that the data is not current in NVRAM FM 151B and will thus retrieve it from near memory acting as a FM cache 150B and send it to the NVRAM controller 332. The NVRAM controller 332 looks up the PDA for the system memory address and then writes the data to the NVRAM FM 151B.

In FIG. 3, the NVRAM controller 332 is shown connected to the FM 151B, NVRAM mass storage 152A, and BIOS NVRAM 172 using three separate lines. This does not necessarily mean, however, that there are three separate physical buses or communication channels connecting the NVRAM controller 332 to these portions of the NVRAM 142. Rather, in some embodiments, a common memory bus or other type of bus is used to communicatively couple the NVRAM controller 332 to the FM 151B, NVRAM mass storage 152A, and BIOS NVRAM 172. For example, in one embodiment, the three lines in FIG. 3 represent a bus, such as a memory bus (e.g., a DDR3, DDR4, etc, bus), over which the NVRAM controller 332 implements a (e.g., out-of-order) protocol to communicate with the NVRAM 142. The NVRAM controller 332 may also communicate with the NVRAM 142 over a bus supporting a native protocol such as a PCI express bus, desktop management interface (DMI) bus, or any other type of bus utilizing an out-of-order protocol and a small enough payload size (e.g., cache line size such as 64 or 128 byte).

In one embodiment, computer system 300 includes integrated memory controller (IMC) 331 which performs the central memory access control for processor 310, which is coupled to: 1) a memory-side cache (MSC) controller 124 to control access to near memory (NM) acting as a far memory cache 150B; and 2) a NVRAM controller 332 to control access to NVRAM 142. Although illustrated as separate units in FIG. 3, the MSC controller 124 and NVRAM controller 332 may logically form part of the IMC 331.

In the illustrated embodiment, the MSC controller 124 includes a set of range registers 336 which specify the mode of operation in use for the NM acting as a far memory cache 150B (e.g., write-back caching mode, near memory bypass mode, etc, described above). In the illustrated embodiment, DRAM 144 is used as the memory technology for the NM acting as cache for far memory 150B. In response to a memory access request, the MSC controller 124 may determine (depending on the mode of operation specified in the range registers 336) whether the request can be serviced from the NM acting as cache for FM 150B or whether the request must be sent to the NVRAM controller 332, which may then service the request from the far memory (FM) portion 151B of the NVRAM 142.

In an embodiment where NVRAM 142 is implemented with PCMS, NVRAM controller 332 is a PCMS controller that performs access with protocols consistent with the PCMS technology. As previously discussed, the PCMS memory is inherently capable of being accessed at the granularity of a byte. Nonetheless, the NVRAM controller 332 may access a PCMS-based far memory 151B at a lower level of granularity such as a cache line (e.g., a 64-bit or 128-bit cache line) or any other level of granularity consistent with the memory subsystem. The underlying principles of the invention are not limited to any particular level of granularity for accessing a PCMS-based far memory 151B. In general, however, when PCMS-based far memory 151B is used to form part of the system address space, the level of granularity will be higher than that traditionally used for other non-volatile storage technologies such as FLASH, which can only perform rewrite and erase operations at the level of a “block” (minimally 64 Kbyte in size for NOR FLASH and 16 Kbyte for NAND FLASH).

In the illustrated embodiment, NVRAM controller 332 can read configuration data to establish the previously described modes, sizes, etc. for the NVRAM 142 from decode table 333, or alternatively, can rely on the decoding results passed from IMC 331 and I/O subsystem 315. For example, at either manufacturing time or in the field, computer system 300 can program decode table 333 to mark different regions of NVRAM 142 as system memory, mass storage exposed via SATA interfaces, mass storage exposed via USB Bulk Only Transport (BOT) interfaces, encrypted storage that supports TPM storage, among others. The means by which access is steered to different partitions of NVRAM device 142 is via a decode logic. For example, in one embodiment, the address range of each partition is defined in the decode table 333. In one embodiment, when IMC 331 receives an access request, the target address of the request is decoded to reveal whether the request is directed toward memory, NVRAM mass storage, or I/O. If it is a memory request, IMC 331 and/or the MSC controller 124 further determines from the target address whether the request is directed to NM as cache for FM 150B or to FM 151B. For FM 151B access, the request is forwarded to NVRAM controller 332. IMC 331 passes the request to the I/O subsystem 115 if this request is directed to I/O (e.g., non-storage and storage I/O devices). I/O subsystem 115 further decodes the address to determine whether the address points to NVRAM mass storage 152A, BIOS NVRAM 172, or other non-storage or storage I/O devices. If this address points to NVRAM mass storage 152A or BIOS NVRAM 172, I/O subsystem 115 forwards the request to NVRAM controller 332. If this address points to TMP NVRAM 173, I/O subsystem 115 passes the request to TPM 334 to perform secured access.

The presence of a new memory architecture such as described herein provides for a wealth of new possibilities. Although discussed at much greater length further below, some of these possibilities are quickly highlighted immediately below.

According to one possible implementation, NVRAM 142 acts as a total replacement or supplement for traditional DRAM technology in system memory. In one embodiment, NVRAM 142 represents the introduction of a second-level system memory (e.g., the system memory may be viewed as having a first level system memory comprising near memory as cache 150B (part of the DRAM device 340) and a second level system memory comprising far memory (FM) 151B (part of the NVRAM 142).

According to some embodiments, NVRAM 142 acts as a total replacement or supplement for the flash/magnetic/optical mass storage 152B. As previously described, in some embodiments, even though the NVRAM 152A is capable of byte-level addressability, NVRAM controller 332 may still access NVRAM mass storage 152A in blocks of multiple bytes, depending on the implementation (e.g., 64 Kbytes, 128 Kbytes, etc.). The specific manner in which data is accessed from NVRAM mass storage 152A by NVRAM controller 332 may be transparent to software executed by the processor 310. For example, even through NVRAM mass storage 152A may be accessed differently from Flash/magnetic/optical mass storage 152A, the operating system may still view NVRAM mass storage 152A as a standard mass storage device (e.g., a serial ATA hard drive or other standard form of mass storage device).

In an embodiment where NVRAM mass storage 152A acts as a total replacement for the flash/magnetic/optical mass storage 152B, it is not necessary to use storage drivers for block-addressable storage access. The removal of storage driver overhead from storage access can increase access speed and save power. In alternative embodiments where it is desired that NVRAM mass storage 152A appears to the OS and/or applications as block-accessible and indistinguishable from flash/magnetic/optical mass storage 152B, emulated storage drivers can be used to expose block-accessible interfaces (e.g., Universal Serial Bus (USB) Bulk-Only Transfer (BOT), 1.0; Serial Advanced Technology Attachment (SATA), 3.0; and the like) to the software for accessing NVRAM mass storage 152A.

In one embodiment, NVRAM 142 acts as a total replacement or supplement for firmware memory such as BIOS flash 362 and TPM flash 372 (illustrated with dotted lines in FIG. 3 to indicate that they are optional). For example, the NVRAM 142 may include a BIOS NVRAM 172 portion to supplement or replace the BIOS flash 362 and may include a TPM NVRAM 173 portion to supplement or replace the TPM flash 372. Firmware memory can also store system persistent states used by a TPM 334 to protect sensitive system information (e.g., encryption keys). In one embodiment, the use of NVRAM 142 for firmware memory removes the need for third party flash parts to store code and data that are critical to the system operations.

Continuing then with a discussion of the system of FIG. 3, in some embodiments, the architecture of computer system 100 may include multiple processors, although a single processor 310 is illustrated in FIG. 3 for simplicity. Processor 310 may be any type of data processor including a general purpose or special purpose central processing unit (CPU), an application-specific integrated circuit (ASIC) or a digital signal processor (DSP). For example, processor 310 may be a general-purpose processor, such as a Core™ i3, i5, i7, 2 Duo and Quad, Xeon™, or Itanium™ processor, all of which are available from Intel Corporation, of Santa Clara, Calif. Alternatively, processor 310 may be from another company, such as ARM Holdings, Ltd, of Sunnyvale, Calif., MIPS Technologies of Sunnyvale, Calif., etc. Processor 310 may be a special-purpose processor, such as, for example, a network or communication processor, compression engine, graphics processor, co-processor, embedded processor, or the like. Processor 310 may be implemented on one or more chips included within one or more packages. Processor 310 may be a part of and/or may be implemented on one or more substrates using any of a number of process technologies, such as, for example, BiCMOS, CMOS, or NMOS. In the embodiment shown in FIG. 3, processor 310 has a system-on-a-chip (SOC) configuration.

In one embodiment, the processor 310 includes an integrated graphics unit 311 which includes logic for executing graphics commands such as 3D or 2D graphics commands. While the embodiments of the invention are not limited to any particular integrated graphics unit 311, in one embodiment, the graphics unit 311 is capable of executing industry standard graphics commands such as those specified by the Open GL and/or Direct X application programming interfaces (APIs) (e.g., OpenGL 4.1 and Direct X 11).

The processor 310 may also include one or more cores 101-104, although a single core is illustrated in FIG. 3, again, for the sake of clarity. In many embodiments, the core(s) 101-104 includes internal functional blocks such as one or more execution units, retirement units, a set of general purpose and specific registers, etc. If the core(s) are multi-threaded or hyper-threaded, then each hardware thread may be considered as a “logical” core as well. The cores 101-104 may be homogenous or heterogeneous in terms of architecture and/or instruction set. For example, some of the cores may be in order while others are out-of-order. As another example, two or more of the cores may be capable of executing the same instruction set, while others may be capable of executing only a subset of that instruction set or a different instruction set.

The processor 310 may also include one or more caches, such as cache 313 which may be implemented as a SRAM and/or a DRAM. In many embodiments that are not shown, additional caches other than cache 313 are implemented so that multiple levels of cache exist between the execution units in the core(s) 101-104 and memory devices 150B and 151B. For example, the set of shared cache units may include an upper-level cache, such as a level 1 (L1) cache, mid-level caches, such as level 2 (L2), level 3 (L3), level 4 (L4), or other levels of cache, an (LLC), and/or different combinations thereof. In different embodiments, cache 313 may be apportioned in different ways and may be one of many different sizes in different embodiments. For example, cache 313 may be an 8 megabyte (MB) cache, a 16 MB cache, etc. Additionally, in different embodiments the cache may be a direct mapped cache, a fully associative cache, a multi-way set-associative cache, or a cache with another type of mapping. In other embodiments that include multiple cores, cache 313 may include one large portion shared among all cores or may be divided into several separately functional slices (e.g., one slice for each core). Cache 313 may also include one portion shared among all cores and several other portions that are separate functional slices per core.

The processor 310 may also include a home agent 314 which includes those components coordinating and operating core(s) 101-104. The home agent unit 314 may include, for example, a power control unit (PCU) and a display unit. The PCU may be or include logic and components needed for regulating the power state of the core(s) 101-104 and the integrated graphics unit 311. The display unit is for driving one or more externally connected displays.

As mentioned, in some embodiments, processor 310 includes an integrated memory controller (IMC) 331, near memory cache (MSC) controller, and NVRAM controller 332 all of which can be on the same chip as processor 310, or on a separate chip and/or package connected to processor 310. DRAM device 144 may be on the same chip or a different chip as the IMC 331 and MSC controller 124; thus, one chip may have processor 310 and DRAM device 144; one chip may have the processor 310 and another the DRAM device 144 and (these chips may be in the same or different packages); one chip may have the core(s) 101-104 and another the IMC 331, MSC controller 124 and DRAM 144 (these chips may be in the same or different packages); one chip may have the core(s) 101-104, another the IMC 331 and MSC controller 124, and another the DRAM 144 (these chips may be in the same or different packages); etc.

In some embodiments, processor 310 includes an I/O subsystem 115 coupled to IMC 331. I/O subsystem 115 enables communication between processor 310 and the following serial or parallel I/O devices: one or more networks 336 (such as a Local Area Network, Wide Area Network or the Internet), storage I/O device (such as flash/magnetic/optical mass storage 152B, BIOS flash 362, TPM flash 372) and one or more non-storage I/O devices 337 (such as display, keyboard, speaker, and the like). I/O subsystem 115 may include a platform controller hub (PCH) (not shown) that further includes several I/O adapters 338 and other I/O circuitry to provide access to the storage and non-storage I/O devices and networks. To accomplish this, I/O subsystem 115 may have at least one integrated I/O adapter 338 for each I/O protocol utilized. I/O subsystem 115 can be on the same chip as processor 310, or on a separate chip and/or package connected to processor 310.

I/O adapters 338 translate a host communication protocol utilized within the processor 310 to a protocol compatible with particular I/O devices. For flash/magnetic/optical mass storage 152B, some of the protocols that I/O adapters 338 may translate include Peripheral Component Interconnect (PCI)-Express (PCI-E), 3.0; USB, 3.0; SATA, 3.0; Small Computer System Interface (SCSI), Ultra-640; and Institute of Electrical and Electronics Engineers (IEEE) 1394 “Firewire;” among others. For BIOS flash 362, some of the protocols that I/O adapters 338 may translate include Serial Peripheral Interface (SPI), Microwire, among others. Additionally, there may be one or more wireless protocol I/O adapters. Examples of wireless protocols, among others, are used in personal area networks, such as IEEE 802.15 and Bluetooth, 4.0; wireless local area networks, such as IEEE 802.11-based wireless protocols; and cellular protocols.

In some embodiments, the I/O subsystem 115 is coupled to a TPM control 334 to control access to system persistent states, such as secure data, encryption keys, platform configuration information and the like. In one embodiment, these system persistent states are stored in a TMP NVRAM 173 and accessed via NVRAM controller 332.

In one embodiment, TPM 334 is a secure micro-controller with cryptographic functionalities. TPM 334 has a number of trust-related capabilities; e.g., a SEAL capability for ensuring that data protected by a TPM is only available for the same TPM. TPM 334 can protect data and keys (e.g., secrets) using its encryption capabilities. In one embodiment, TPM 334 has a unique and secret RSA key, which allows it to authenticate hardware devices and platforms. For example, TPM 334 can verify that a system seeking access to data stored in computer system 300 is the expected system. TPM 334 is also capable of reporting the integrity of the platform (e.g., computer system 300). This allows an external resource (e.g., a server on a network) to determine the trustworthiness of the platform but does not prevent access to the platform by the user.

In some embodiments, I/O subsystem 315 also includes a Management Engine (ME) 335, which is a microprocessor that allows a system administrator to monitor, maintain, update, upgrade, and repair computer system 300. In one embodiment, a system administrator can remotely configure computer system 300 by editing the contents of the decode table 333 through ME 335 via networks 336.

For convenience of explanation, the application may sometimes refers to NVRAM 142 as a PCMS device. A PCMS device includes multi-layered (vertically stacked) PCM cell arrays that are non-volatile, have low power consumption, and are modifiable at the bit level. As such, the terms NVRAM device and PCMS device may be used interchangeably in the following discussion. However it should be realized, as discussed above, that different technologies besides PCMS may also be utilized for NVRAM 142.

It should be understood that a computer system can utilize NVRAM 142 for system memory, mass storage, firmware memory and/or other memory and storage purposes even if the processor of that computer system does not have all of the above-described components of processor 310, or has more components than processor 310.

In the particular embodiment shown in FIG. 3, the MSC controller 124 and NVRAM controller 332 are located on the same die or package (referred to as the CPU package) as the processor 310. In other embodiments, the MSC controller 124 and/or NVRAM controller 332 may be located off-die or off-CPU package, coupled to the processor 310 or CPU package over a bus such as a memory bus (like a DDR bus (e.g., a DDR3, DDR4, etc)), a PCI express bus, a desktop management interface (DMI) bus, or any other type of bus.

Far Side Memory Used for Transactional Multi-Threaded Software and Non Transactional Software

Processor designers are currently designing enhanced instruction sets that enable “transactional” support of multi-threaded software. In conventional (i.e. non transactional) multithreaded software, programs protect data with “locks.” Only one thread can hold a lock at any one time, so it can ensure that no other thread is modifying the data at the same time. This tends to be pessimistic: the thread with the lock prevents any threads from taking the lock, even if they only want to read the data or make a non-conflicting update to it.

With transactional support, referring to FIG. 4, threads no longer need to take out locks when manipulating data. They start a transaction 401, make their changes 402, and when they've finished, commit the transaction 403 or roll back 404 the changes made at step 402 if the transaction cannot be committed. While the thread is making its changes 402 over the course of the transaction, referring to FIG. 5, special hardware 570 within the processor 510 takes note of any/all cache 513 and near memory 550B locations that the thread reads from and writes to.

Typically, any/all data writes made by a transaction are present in cache simply because a cache holds a system's most recent changes. That is, if a transaction needs to change a data item, the data item is called up from deeper storage if it is not in cache already, changed, and then written into cache. Thus, assuming the amount of data changes made by a transaction are limited to being less than the cache size available for each data address, all changes made by a transaction will be present in cache. Hardware within the processor prevents write-back of these changed data items to persistence until commitment of the transaction. In a first embodiment, the cache referred to above includes processor caches and near memory. In a second embodiment, the cache referred to above only includes processor caches (i.e., near memory is not included). For simplicity, the remainder of the document will refer mainly to the first embodiment.

In an embodiment, there is an instance of special hardware 570 for each CPU core 501-504 within the processor 510 and/or each instruction execution pipeline within each CPU core within the processor 510. Here, the special hardware 570 instance (e.g., as implemented with logic circuitry) of the core/pipeline that is executing the transactional thread takes note of the transaction's cache and near memory reads and writes as described above. Note that some caching levels within processor 510 may service multiple cores (e.g., a last level cache) while other caching levels within processor 510 may service only a single core (e.g., a core's L1 cache).

When the transaction is ready to be committed, the special hardware 570 checks that while the transaction was executing no other thread made any changes to or read from these same locations. If this condition is met, the transaction is committed 403 and the thread continues. Here, committing the changes means the changes are written into persistence storage. If this condition is not met, the transaction is aborted, and all its changes are undone 404. In one embodiment, in order to “undo” the changes, fresh data representing the state of the data before any changes made by the transaction are called up from persistence storage and rewritten into cache, or, the cache lines that were changed are invalidated. The thread can then retry the operation, try a different strategy (for example, one that uses locks), or give up entirely.

In an implementation, NVRAM far memory 551B corresponds to “persistence” storage to which committed data changes are stored upon commitment of a transaction, while, near memory 550B and any/all caches 513 above near memory correspond to the cache locations where a thread is able to make changes prior to commitment of its transaction.

The concept of persistence storage in various cases, however, can be extended to other types of software processes that do not technically meet the definition of a transaction as discussed above. Persistence storage, according to various different information processing paradigms, may be a writable data store whose records reflect the formally recognized state of some process or data structure (and is therefore globally visible, e.g.), and/or, have some expectation of being needed over a extended time span (e.g., multiple on/off cycles of the computing system). Notably, many such software processes may also choose to implement persistence storage in NVRAM far memory 551B.

For those non transactional software processes that recognize the existence of persistence storage, the software has to have embedded precautions that ensure modified data that needs to be persisted is flushed from cache and stored to persistent storage before any subsequent changes are made to it. Here, for example, if a change is made to an item of data and the software views the change as needing to be reflected in persistent storage, the software will insert a cache line flush instruction (e.g., CLFLUSH) followed by a memory fence instruction (e.g., MFENCE). The cache line flush instruction will cause the newly changed data to be written back to persistence storage 551B. The memory fence instruction will prevent other operations of the same thread from accessing the data until it has been written to persisted storage 551B.

In more complicated approaches, the thread's software includes complicated book keeping tasks to keep track of what data items in cache need to be persisted to persistence storage 551B. Here, for example, certain data items may be recognized by the thread's software as requiring persistence, the book keeping software will keep track of these data items and, at an appropriate moment in the code's execution, execute appropriate cache line and memory fence instructions.

FIG. 6 shows an improved approach where the special hardware 570 of FIG. 5 is also used, not only to support the roll back of transactions as discussed above with respect to FIG. 4 but also to eliminate the need for the software book keeping function described just above.

As observed in FIG. 6, the software is only asked to define a persistent region of code. This definition is marked at the beginning of the region with a PBEGIN instruction 601 and at the end of the region with a PEND instruction 604. The PBEGIN instruction essentially “turns on” 602 the functionality of the special hardware 570. While the code is executing after the PBEGIN instruction, the special hardware 570 tracks 603 which cache lines were changed. When the PEND instruction 604 is executed it causes the cache lines identified by the special hardware 570 to be flushed 605 to persistence 551B and turns off the special hardware 570. No other instructions are permitted to be executed after the PEND instruction until all cache lines are flushed to effect the memory fence.

Thus the special hardware 570 tracks cache accesses not only during transactional operations but also during non transactional operations. FIG. 5 shows a representation of an instruction execution pipeline 580 within a core that is coupled to the special hardware 570. Here the coupling is used to turn on the special hardware 570 in response to a PBEGIN instruction and turn off the special hardware in response to a PEND instruction. The instruction execution pipeline is also designed with logic to prevent issuance of a next instruction until the cache flushing is complete. Cache flushing logic is also coupled to the instruction execution pipeline and the special hardware but is not drawn for convenience. The cache flushing logic is triggered into action by the PEND instruction and refers to the special hardware 570 to understand which cache lines need to be flushed. Other features of FIG. 5 are as described above with respect to FIG. 3.

FIG. 7 shows an integrated methodology that depicts both functions of the specialized hardware. Unless a transactional operation begins or PBEGIN instruction is executed, the specialized hardware 551B remains idle 701.

If a transaction operation begins, the specialized hardware 570 is enabled and begins tracking which cache lines are modified by the transaction 702. When the transaction is complete, transactional hardware 571 within the processor checks to see whether any other transactions have written to or read from these same cache lines 703. If none have, the changes are committed 704 to far memory NVRAM 551B, otherwise, the cache lines are replaced with content from persistence NVRAM 551B or invalidated 705.

If a PBEGIN instruction is executed, the specialized hardware 570 is enabled and begins tracking which cache lines are modified by the software process 706. When a PEND instruction is executed, all modified cache data is written back to persistence NVRAM 551B and no other instructions are permitted to execute until the write back is complete 707.

FIG. 8 shows a compilation process to be performed by a compiler. As observed in FIG. 8, the compilation process identifies 801 the beginning of a region of code after which any data changes made by the code are to be persisted to persistence storage. In response to the identification 801, the compilation code inserts 802 a PBEGIN instruction into the program code or marks the location in the code where the PBEGIN instruction is to be inserted. The compilation process also identifies 803 the beginning of a region of code after where the PBEGIN instruction is (or is to be) inserted whose data changes do not need to be persisted. In response to the identification 803 of the second region of code, the compilation process inserts a PEND instruction (or marks where a PEND instruction is to be inserted) into the program code after the last data change that needs to be persisted but before the first data change that does not need to be persisted.

Processes taught by the discussion above may be performed with program code such as machine-executable instructions which cause a machine (such as a “virtual machine”, a general-purpose CPU processor or processing core disposed on a semiconductor chip or special-purpose processor disposed on a semiconductor chip) to perform certain functions. Alternatively, these functions may be performed by specific hardware components that contain hardwired logic for performing the functions, or by any combination of programmed computer components and custom hardware components.

A storage medium may be used to store program code. A storage medium that stores program code may be embodied as, but is not limited to, one or more memories (e.g., one or more flash memories, random access memories (static, dynamic or other)), optical disks, CD-ROMs, DVD ROMs, EPROMs, EEPROMs, magnetic or optical cards or other type of machine-readable media suitable for storing electronic instructions. Program code may also be downloaded from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a propagation medium (e.g., via a communication link (e.g., a network connection)).

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 

1. A processor, comprising: an interface to non volatile random access memory; logic circuitry to: identify cache lines modified by a transaction which views said non volatile random access memory as said transaction's persistence storage; and, identify cache lines modified by a software process other than a transaction that also views said non volatile random access memory as persistence storage.
 2. The processor of claim 1 wherein said non volatile random access memory is PCM.
 3. The processor of claim 2 wherein said non volatile random access memory is PCMS.
 4. The processor of claim 1 further comprising an instruction execution pipeline to execute a first instruction of said software process that identifies a starting point of said software process's code and execute a second instruction of said software process that identifies an ending point of said software process's code, wherein data changes made by said software process between said starting point and ending point are to be persisted to said volatile random access memory, said instruction execution pipeline coupled to said logic circuitry to enable said logic circuitry in response to said first instruction and disable said logic circuitry in response to said second instruction.
 5. The processor of claim 4 wherein said processor comprising cache flushing circuitry coupled to said instruction execution pipeline and said logic circuitry.
 6. The processor of claim 5 wherein said instruction execution pipeline will not execute a next instruction until said cache flushing circuitry has completed flushing cache lines identified by said logic circuitry to said non volatile random access memory in response to said second instruction.
 7. A method, comprising: executing a transaction on a processor where said executing of said transaction includes making changes to items of data, said changes kept in one or more caching levels, tracking where said changes reside in said one or more caching levels with hardware of said processor, determining if said changes are to be committed to a non-volatile random access memory, and persisting said changes to said non-volatile random access memory upon commitment or rolling back said changes; executing a software process on said processor that marks a beginning and an end of a region of said software process where data changes made by said software process are to be persisted, tracking changes made by said software process between said beginning and said end with said hardware, and writing said changes made by said software process to said non-volatile random access memory upon said end of said region being reached.
 8. The method of claim 7 wherein said beginning is marked with a first instruction and said end is marked with a second instruction.
 9. The method of claim 7 wherein said non-volatile random access memory is implemented with PCM.
 10. The method of claim 9 wherein said non-volatile random access memory is implemented with PCMS.
 11. The method of claim 7 wherein said method further comprises enabling said hardware in response to said first instruction.
 12. The method of claim 11 wherein said method further comprises disabling said hardware in response to said second instruction.
 13. A machine readable storage medium having program code stored thereon that when processed by a computing system causes a method to be performed, said method comprising: identifying a region of code whose data changes need to be persisted to persistence storage; and, marking a beginning and an end of said region with first and second instructions respectively.
 14. The machine readable medium of claim 13 wherein said first instruction causes a processor to enable hardware that tracks said data changes.
 15. The machine readable medium of claim 14 wherein said second instruction disables said hardware.
 16. The machine readable medium of claim 13 wherein said second instruction causes said data changes to be flushed from one or more cache levels to said persistence storage.
 17. The machine readable medium of claim 16 wherein said second instruction prevents any further instructions being executed until said data changes have completed being flushed to said persistence storage.
 18. The machine readable medium of claim 13 wherein said persistence storage is non volatile random access memory.
 19. The machine readable medium of claim 18 wherein said non volatile random access memory is PCM.
 20. The machine readable medium of claim 19 wherein said non volatile random access memory is PCMS. 